This invention relates to a process and apparatus suitable for controlling the operation of a multiple station document handling machine, for example, a mail inserting machine.
Multiple station inserting machines, for example of the model 3100 series manufactured by Pitney Bowes, Stamford, Conn., perform the function of feeding a plurality of enclosures from different feeders and inserting them into an envelope. When combined with a mailing machine and a power stacker, the machine automatically prepares an envelope for mailing by inserting all the contents into the envelope, sealing the flap of the envelope, and meter stamping the required postage and stacking stuffed envelopes so assembled. For many applications a special high-speed feeder is provided in place of one of the standard feeders for providing the capability of feeding many enclosures during each cycle of the machine. The special high-speed feeder has documents fed therethrough which contain control function indicia thereon, which are scanned to provide control function signals to insure the proper machine timing and control functions. The control function indicia may be printed on one or more rows, the position of the indicia being determined by the row and by the distance from the lead edge of the document which, when scanned, represents a bit weight or specific control function. For example, the appearance of control function indicia on the document at predetermined locations thereon can provide select control feed from feeder Nos. 1, 2, 3, etc., provide for the selection of an even number of pages from the high speed feeder, provide a stop-and-lock function, provide indication of the end of a zip code group and that the envelope which designates the end of the group will be offset on an associated stacker, etc. The control function indicia are accurately spaced from the lead edge of the control function indicia bearing document, as well as accurately spaced with respect to each other. Although all of the control function indicia are accurately printed with respect to one another, and the lead edge of the document, broad tolerances may exist from the lead edge of the document which are caused by poor registration of the document to the printer mechanism which imprints the indicia on the document, improper bursting or uneven edge of the document after printing, poorly folded documents or documents skewed through the feeder in cases where the lead edge of the edge detection circuitry is not in line with the direction of feed of the control function indicia on the document. Of course, the aforesaid problems could produce errors in reading the control function indicia. In reading the control function indicia, scanning zones or data windows are generally provided to read predetermined data bits within given time intervals. Traditionally, data windows are provided by timing the document through the high-speed feeder, by printing a timing track adjacent to the data bit, or by generating a series of sequential lead edge detectors to coincide with the data bits. Timing the document through the feeder has the disadvantage of variation in time caused by the tolerance and the ambient conditions on the timing circuits and the change in speed caused by the speed variations in the feeder itself. The printing timing track is a very accurate method of determining bit windows, but has the disadvantage of requiring additional computer print time, regardless of the presence of data, since every line of print must be made by the line printer. The printed timing track also requires an extra and costly reader. Sequential edge detection is a relatively low cost technique, but requires critical adjustment in alignment of the edge detectors, and makes no allowances for print distance variations from the edge of the document.